The corrosion behaviors of carbon steel under the effect of AC and imidazoline quaternary ammonium salt corrosion inhibitor

The development of self-healing coating technology makes the corrosion inhibitor can be used in preventing the external corrosion of the pipelines, providing a new possibility that the corrosion behaviors of carbon steel are under the effect of the corrosion inhibitor and alternating current (AC). Understanding the combined effect of the corrosion inhibitor and AC on the corrosion behavior is essential. In this paper, the corrosion behaviors of X90 steel under the effect of AC and imidazoline quaternary ammonium salt corrosion inhibitor (IM) were investigated by electrochemical measurements and surface analysis. The results showed that the adsorption of the IM on the corrosion surface influenced the AC corrosion behaviors. Meanwhile, the adsorption process of IM was under the effect of AC interference. The negative shift of the potential induced at low AC current density could enhance IM absorption, causing a decrease in the corrosion current density. As AC current density further increased, IM tended to desorb with the formation of the corrosion product, resulting in an increase in the corrosion current density. The high IM concentration cannot effectively decrease the AC-induced corrosion rate, which was probably because the anodic desorption due to the positive shift of the potential occurred at the high IM concentration. As the IM concentration increased, the active substances in corrosion products such as gamma-FeO (OH) and Fe3O4 gradually decreased, while alpha-FeO(OH) increased, indicating the protectiveness of the outer rust layer increased with the IM concentration.